Light curing restorative materials has been used in dentistry for over 20 years. Typically the dentist prepares a tooth as he would for a silver amalgam restoration but substitutes a light curable restorative material, which is cured by exposure to light generated from a curing unit light at a wavelength in the 400–500 nm range. In the past, various attempts have been made to adjust for the proper occlusal contour of the restoration as well as the bonding of the restoration to the tooth itself, both to the dentin and to the enamel. Despite efforts of the dentist, micro leakage remains a major problem and occurs when either the filling material is not well adapted to the cavity walls or the restoration shrinks in the curing process to something less than the size of the prepared cavity into which the material is placed. At the microscopic level this results in an open margin between the restorative material and the tooth structure and in turn provides a site for bacterial invasion and subsequent breakdown of the restorative material as well as caries or tooth decay in the tooth structure itself.
In the industrial field, by comparison, when plastic or plastic like materials are molded, they are always molded under pressure and in so doing the material is caused to adapt very closely to the mold cavity. The concept of applying pressure to a photo curable material simultaneously with the application of light to improve adaptation during polymerization is taught in U.S. Pat. No. 4,571,188 (Hamilton). This patent teaches fabricating a transparent occlusal matrix, which is placed over the light curable composite before pressure is applied to the matrix. The composite is then cured by passing light through the transparent matrix. However, it is necessary to specifically fabricate a custom transparent occlusal matrix to match the occlusal surfaces of each restoration, which is time consuming, cumbersome and inconvenient. Moreover, it is difficult to cause adequate external pressure to be applied to the occlusal surface through the transparent matrix and to have a significant effect on the compression of the restorative material.
Another method for applying pressure to a photo curable material simultaneously with the application of light is taught in U.S. Pat. No. 5,759,032 (Bartel) through use of an accessory adapted to fit over the light-emitting tip of a light guide. This approach however does not address the problem of occlusal contact with the opposing dental arch which will differ for every patient so that once the restoration is polymerized the teeth can come into normal occlusal contact. In addition, the pressure applied to the restoration is limited by the fragility of the conventional glass light guides in common use today. Furthermore, it is awkward and difficult to generate sufficient pressure through the handle of a dental light gun or wand to create a significant effect on the compression of the dental restorative material.
Yet another method for curing photo curable composites under light while applying pressure is taught in U.S. Pat. No. 5,104,591 (Massuhara et al) but is limited to an application in a dental laboratory when creating a mold from an impression and is designed only for use outside the mouth. This method is not adaptable for use by a dentist to the clinical restoration of a tooth within a patient's mouth.